Some known vehicles measure speeds at which the vehicles travel (e.g., vehicle speeds) based on diameters of one or more wheels and the rates at which the wheels rotate. For example, in some locomotives, a diameter of a wheel associated with a designated axle (e.g., the second axle of a six axle locomotive) may be manually measured by an operator of the locomotive. The speed of the locomotive is then monitored and displayed to the operator by multiplying the diameter of the wheel by the speed at which the wheel rotates.
The diameter of the wheel may be incorrect. For example, the manual measurement of the diameter may result in an incorrect measurement due to human error, the measured diameter may be incorrectly entered into a control system of the vehicle (that calculates the vehicle speed), and/or software updates to the control system may result in previously entered diameters being erased or otherwise lost.
Incorrect wheel diameters can result in erroneous reporting of the vehicle speed to the operator. For example, with respect to an actual wheel diameter of 42 inches, a one inch error in the measurement of the diameter can result in an error of 2.38% in the reporting of the vehicle speed at an actual vehicle speed of 70 miles per hour (or 112.5 kilometers per hour). Such an error can cause the vehicle speed that is reported to the operator to be off by approximately 1.66 miles per hour (or 2.67 kilometers per hour). A three inch error in the measurement of the diameter can result in an error of 7.14% in the reporting of the vehicle speed at an actual vehicle speed of 70 miles per hour (or 112.5 kilometers per hour). Such an error can cause the vehicle speed that is reported to the operator to be off by approximately five miles per hour (or eight kilometers per hour).
The reporting of incorrect vehicle speeds can pose a safety threat, such as where the reported vehicle speed is slower than the actual speed of the vehicle. As a result, a need exists to identify erroneous vehicle speeds.